FIG. 1 is a vertical-sectional view illustrating a conventional fan-motor for a vacuum cleaner. Referring to FIG. 1, in the conventional fan-motor for the vacuum cleaner, a motor 4 composed of a stator 2 and a rotor 3 is installed in a motor housing 1 having its upper portion opened, and a rotation shaft 5 is fit-pressed into the center portion of the rotor 3 in the up/down direction, and rotated with the rotor 3, for transmitting power.
An opening unit of an impeller casing 6 having a suction hole 6a on its top surface is coupled to the upper opening unit of the motor housing 1. An impeller 7 coupled to the top end of the rotation shaft 5 for sucking the air through the suction hole 6a is installed inside the impeller casing 6. A guide vane 8 for guiding the air sucked into the impeller casing 6 by the impeller 7 to the motor side 4 is installed at the lower portion of the impeller 7.
The guide vane 8 includes a body unit 9 formed in a circular planar shape with a predetermined thickness and area, a plurality of diffuser vanes 10 installed on the edges of the top surface of the body unit 9 at regular intervals, for raising a pressure of the air passing through the impeller 7, and a plurality of return vanes 11 installed on the bottom surface of the body unit 9, for guiding the air pressure-raised by the diffuser vanes 10 to the motor side 4.
In the conventional fan-motor for the vacuum cleaner, when power is applied to the motor 4, rotation force is generated in the rotor 3, for rotating the rotor 3. The rotation shaft 5 is rotated with the rotor 3.
When the rotation shaft 5 is rotated, the impeller 7 coupled to the top end of the rotation shaft 5 is rotated, to generate suction force. By the suction force, the air is sucked into the impeller casing 6 through the suction hole 6a of the impeller casing 6. The sucked air passes through the impeller 7, and is discharged to the lateral direction of the impeller 7.
The pressure of the air passing through the impeller 7 is raised by the diffuser vanes 10 of the guide vane 8. The air having the raised pressure is supplied to the lower side return vanes 11 through space units 12 between the inner circumference of the impeller casing 6 and the outer circumference of the guide vane 8, guided to the center portion by the return vanes 11, and sent to the motor side 4. Accordingly, the motor 4 is cooled and the air is discharged.
The impeller 7 and the flow of the sucked air passing through the impeller 7 will now be explained with reference to FIGS. 2 and 3.
FIG. 2 is a perspective view illustrating a general 2-dimensional (2D) impeller, and FIG. 3 is a partial cross-sectional view provided to explain a flow passing through the impeller of FIG. 2.
As illustrated in FIG. 2, the impeller 7 includes a top plate 7a having a suction hole 7a′ at its center portion to communicate with an impeller casing 6 to suck the air, a bottom plate 7b being disposed to overlap with the top plate 7a, and having a shaft hole 7b′ at its center portion so that a rotation shaft 5 can be inserted into the shaft hole 7b′, and a plurality of blades 7c disposed between the top plate 7a and the bottom plate 7b, isolated from each other in the circumferential direction at regular intervals, and extended in the radial direction. Since the impeller 7 induces a 2D flow, it is called the 2D impeller.
As shown in FIG. 3, in a fan-motor for a vacuum cleaner using the 2D impeller 7, the air flow sucked into the suction hole 7a′ of the top plate 7a through a suction hole 6a (refer to FIG. 1) of the impeller casing 6 is not smoothly transferred to the blade sides 7c due to weak induction in the suction hole 7a′. That is, a suction flow loss occurs in the suction hole side 7a′. 
In general, if a fluid flow undergoes a direction change or a sudden shape change, a flow loss is caused by a change degree. In the case of the 2D impeller 7, the sucked flow is bent at an angle of almost 90° and sent to gaps between the blades 7c (refer to arrows).
A 3D impeller generally known to be suitable for high speed rotation (over 70,000 rpm) can be used to overcome the flow loss by inducing a 3D flow. It will be explained below with reference to FIG. 4.
FIG. 4 is a perspective view illustrating a general 3D impeller, and FIG. 5 is a partial cross-sectional view provided to explain a flow passing through the impeller of FIG. 4.
As depicted in FIG. 4, the 3D impeller 7′ includes a main body 7′a having a shaft hole 7′c into which a rotation shaft 5 is coupled, and a plurality of blades 7′b arranged along the outer circumference of the main body 7′a having predetermined curvature, and isolated from each other with their upper portions bent.
As shown in FIG. 5, in the 3D impeller 7′ applied to a fan-motor for a vacuum cleaner, the inducer unit formed by bending the upper portions of the blades 7′b straightens a sucked fluid and pushes the fluid to a target direction, namely, to diffuser vane sides 10 disposed to surround the impeller 7′. This configuration reduces a flow loss in a suction hole side 6′a of an impeller casing 6′ and facilitates a flow to the diffuser vane sides 10.
However, as illustrated in the above drawings, the 3D impeller 7′ is higher than the 2D impeller 7, thereby increasing the size of the impeller casing 6′. As a result, the size of the fan-motor for the vacuum cleaner increases, and the whole size of the vacuum cleaner increases.